1. Field of the Invention
This invention relates generally to contamination protective devices and more particularly to an improved boot structure of the type which protects telescopically reciprocal devices, such as shock absorbers, from contamination.
2. Description of the Prior Art
Telescopically reciprocal mechanisms, such as linear, or automotive-type shock absorbers, are subject to damage and premature failure resulting from contaminants such as sand and dirt which are carried by the axially extensible member past the seals into the housing during retracting movements of the mechanism. To prevent, or at least substantially reduce, this type of mechanism failure, contamination protective boot structures have long been employed to enclose the seal area of the housing and at least a part of the extensible member. Protective boots used for this purpose are normally formed of an elastomeric material and are generally cylindrical, or frusto-conical configuration, with one end attached to the periphery of the housing in a position which is axially set-back from the seal area end of the housing, and the opposite end of the boot is attached either to the extensible member or to the structure to which the extensible member is attached. Since the mechanism being protected is telescopically reciprocal, the protective boots are convoluted along their lengths as in a bellows to allow the boots to be axially extended and contracted along with the mechanism to which they are attached. This same requirement that the boots be capable of axial extension and contraction movements requires that the boots be capable of breathing, i.e., expelling air during retraction and intaking air during extension.
The prior art protective boot structures are attached to the telescopically reciprocal mechanism by plastic tie straps of the type sometimes referred to as cable-ties. The tie straps are circumscribingly wrapped around the ends of the boot and are tightened to seal and frictionally hold the boot in place on the telescopically reciprocal mechanism.
One problem with the tie strap attaching method is that the straps are incrementally adjustable devices and oftentimes one adjusted position will be too loose and due to the lack of sufficient compressibility at the attachment point, the tie strap cannot be tightened enough to reach the next adjustment position of the strap. The end result in a situation of this sort is that the boot is too loose and can axially move on the telescopically reciprocal mechanism.
Other disadvantages with the tie strap attaching method are from a manufacturers standpoint, in addition to the cost of the tie straps, assembling, tightening and cutting off the excess length of the strap consumes expensive assembly time. Also, the tie strap attachment method is less than ideal from a servicing and/or replacement standpoint.
The prior art protective boot structures are provided with breather holes formed at various locations in its convoluted surface. For example, in an average boot used to protect a shock absorber, a minimum of twelve breather holes are provided with each hole being about 0.150 inches in diameter. The needed breather holes weaken the structural integrity of the boot and make it impractical to provide any form of air filtration device. In that the holes are for breathing purposes, contaminants can enter into the boot as a result of normal breathing of the boot. In most situations, contaminant entry into the boot through the breather holes is not a serious problem. However, in some cases, such as when the telescopically reciprocal mechanism is used in very sandy, dusty or otherwise hostile environments, the lack of being able to provide an air filtration device or element can be a drawback.
Therefore, a need exists for a new and improved protective boot structure for use with telescopically reciprocal mechanisms which overcomes some of the problems and shortcomings of the prior art.